1. Field of the Invention
The present invention relates in general to an in-line filter device connected to a compressed air line, and more particularly to such an in-line compressed air filter device having an improved structural arrangement, which permits efficient removal of liquid particles such as water and oil vapor contained in compressed air and which is compact in construction and allows easy maintenance service thereof.
2. Discussion of the Prior Art
Conduits used for supplying compressed air to various pneumatically operated components employed in various factories, atomic plants and medical equipment, for example, are generally provided with an in-line filter device or assembly for removing water and oil vapor contained in the flowing compressed air, for the purpose of protecting the pneumatic components
Various types of such in-line filter devices have been conventionally available. For instance, U.S. Pat. No. 4,487,618 to David O. Mann discloses an in-line filter device called "airline vapor trap", which is capable of removing water and/or oil vapor from a compressed air line, with particularly high efficiency.
Described more specifically, the airline vapor trap disclosed in the above-identified publication includes a first filter having a first pad or packing of wire mesh fibers such as stainless steel fibers, a second filter having a second pad or packing of an absorbent plug structure comprising cottom fibric, for example, and a hollow base which defines an enclosed volume or chamber which communicates with the first and second filters and which is provided with a drain opening. Vapor or liquid particles contained in incoming compressed air are coalesced into droplets while the compressed air is passed through the first filter, and the droplets are trapped within the enclosed chamber of the hollow base. The trapped droplets are discharged through the drain opening. Thus, the vapor or liquid particles are separated from the compressed air. As the compressed air stream thus dried is passed through the second filter, any remaining vapor is vaporized. In this manner, the water and oil vapor, and dust or other foreign matters are effectively removed by the in-line vapor trap or filter device.
For preventing condensation (liquefaction) of a small volume of remaining vapor which has been vaporized, it is desirable to position the in-line filter device at a location along the compressed air conduit, which is relatively near a pneumatic component connected to the conduit. However, the in-line filter device of the type described above tends to be comparatively large-sized, due to a laterally spaced-apart arrangement of the first and second filters in the form of two independent cartridges apart from each other in the direction of length of the airline conduit. Accordingly, the filter device requires a relatively large space for installation. Therefore, there exists a limitation in the location of the filter device that can be selected along the length of the conduit. In other words, it is desirable to construct an in-line filter device as compact as possible. In this respect, there remains some room for improvement in the construction of the in-line filter device of the type disclosed in the above-identified publication.
In the filter device in question, the pads or packings in the first and second filters should be cleaned or replaced with new ones, as the packings are contaminated. In particular, the packing in the second filter should preferably be replaced at a shorter time interval than that in the first packing. However, the laterally spaced-apart first and second filters of the filter assembly shown in the above-identified document are mounted and clamped with a plurality of bolts between an upper cap in the form of a manifold, and a lower cap in the form of the hollow base. When the bolts are removed for removing one of the first and second filter cartridges, the entire assembly is disassembled. Namely, it is difficult to remove only one of the two filter cartridges. Thus, the maintenance service of the filter assembly is comparatively cumbersome.
Further, the droplets separated from the compressed air should be efficiently discharged from the filter device, without lowering the pressure of the compressed air. For this purpose, a drain valve as disclosed in laid-open Publication No. 45-36182 of examined Japanese Patent Application or other suitable draining means is suitably used. The drain valve disclosed in the above publication is automatically placed in its open position for discharging only the liquid consisting of a mass of the trapped droplets, when the volume of the liquid exceeds a predetermined value.
However, the liquid always stays in a given amount in the bottom portion of the housing of the filter device, and tends to be re-vaporized before the liquid is discharged. This means low efficiency of removal of the liquid particles from the compressed air.